Sensitivity of MDM2 amplification and unexpected multiple faint alphoid 12 (alpha 12 satellite sequences) signals in atypical lipomatous tumor

This study assessed whether analysis of MDM2 copy number by fluorescence in situ hybridization (FISH) would help distinguish lipomas from atypical lipomatous tumors, otherwise referred to as well-differentiated liposarcomas, using a commercially available MDM2 FISH kit. 227 lipomatous and 201 non-lipomatous tumors were analyzed to assess its sensitivity and specificity. Of 178 mature lipomatous tumors, 86 were classified histologically as lipoma and 92 as atypical lipomatous tumor. Two of the lipomas harboring MDM2 amplification were reclassified as atypical lipomatous tumors. Overall, 13 atypical lipomatous tumors did not reveal MDM2 or CDK4 amplification, although this was reduced to 12 following analysis of multiple slides. Three of these cases revealed very occasional tumor cells harboring high-level MDM2 amplification, two had a dedifferentiated component, and MDM2 amplification was detected when one tumor recurred. The remaining six cases exhibited reactive/inflammatory features and were reclassified as lipomas. The findings indicate that MDM2 amplification is 93.5% sensitive for diagnosing atypical lipomatous tumor. A total of 2 of the 20 dedifferentiated liposarcomas failed to reveal MDM2 amplification. All atypical lipomatous tumors measured >10?cm, two dedifferentiated liposarcoma presented de novo at <10?cm, and ～50% of lipomas measured >10?cm. Spindle cell lipomas, lipoblastomas, hibernomas and pleomorphic liposarcomas did not reveal MDM2 amplification. Of 201 non-lipomatous tumors, eight revealed MDM2 amplification or multiple faint alphoid 12 signals and were reclassified as dedifferentiated liposarcoma. Multiple faint alphoid 12 signals were observed in nine tumors from seven patients, an observation not previously reported on paraffin sections: these included four atypical lipomatous tumors, and three dedifferentiated liposarcomas, one previously diagnosed as a myxofibrosarcoma, all of which also revealed amplification of CDK4, although two lacked MDM2 amplification. MDM2 FISH test is a useful adjunct to histology for distinguishing lipoma from atypical lipomatous tumor. The limitations of molecular genetic tests must be known before introducing them into a clinical service.     

Evaluation of MDM2 and CDK4 amplification by real-time PCR on paraffin wax-embedded material: a potential tool for the diagnosis of atypical lipomatous tumours/well-differentiated liposarcomas

Atypical lipomatous tumours/well-differentiated liposarcomas and dedifferentiated liposarcomas are characterized by 12q13-15 region amplification. In contrast, this molecular event has not been reported in benign lipomas. Within the 12q13-15 chromosomal region, the MDM2, SAS, HMGA2, and CDK4 genes are the most frequent targets of amplification. A series of lipomas (36 cases) and liposarcomas (48 cases) was analysed for MDM2 and CDK4 gene amplification by real-time PCR. MDM2 and CDK4 gene amplification was detected in 2.8% and 5.6% of lipomas and 98.2% and 82.4% of liposarcomas, respectively. Moreover, co-amplification of the two genes as well as a higher-level amplification was observed more frequently in dedifferentiated liposarcomas than in atypical lipomatous tumours/well-differentiated liposarcomas. Real-time PCR proved to be a fast and reliable method to characterize lipomas and liposarcomas by quantification of MDM2 and CDK4 gene amplification. It is applicable to paraffin wax-embedded tissues and could be useful when histological diagnosis is difficult.     

Inflammatory malignant fibrous histiocytomas and dedifferentiated liposarcomas: histological review, genomic profile, and MDM2 and CDK4 status favour a single entity

Inflammatory malignant fibrous histiocytoma (inflammatory MFH) is a very rare tumour that occurs most often in the retroperitoneum. So far, it has been considered to be a special subtype of MFH. As it is now widely accepted that most retroperitoneal pleomorphic MFHs are dedifferentiated liposarcomas, the present study compared histological features, genomic profile (CGH analysis), and MDM2 and CDK4 status (immunohistochemistry, FISH, and quantitative PCR) in inflammatory MFHs from 12 patients and dedifferentiated liposarcomas that had an inflammatory MFH component from eight patients. Metaphase cytogenetic and FISH analyses were also performed on one inflammatory MFH. Histological review showed areas of well-differentiated liposarcoma in nine inflammatory MFHs. CGH analysis showed 12q13-15 amplification or gain in six of seven inflammatory MFHs and in seven of seven dedifferentiated liposarcomas. Immunohistochemistry showed positivity of tumour cells for MDM2 in every tumour in both groups and for CDK4 in ten and seven inflammatory MFHs and dedifferentiated liposarcomas, respectively. Metaphase cytogenetic and FISH analysis performed on one inflammatory MFH showed the presence of a supernumerary large marker chromosome and ring chromosome with high-level amplification of both MDM2 and CDK4 genes. FISH analysis on paraffin wax-embedded sections showed amplifications of MDM2 and CDK4 in seven of seven inflammatory MFHs and in seven of seven dedifferentiated liposarcomas. Quantitative PCR showed amplification of MDM2 in six and of CDK4 in seven of nine inflammatory MFHs. In conclusion, this study strongly suggests that most so-called inflammatory MFHs are dedifferentiated liposarcomas.     

Utility of fluorescence in situ hybridization to detect MDM2 amplification in liposarcomas and their morphological mimics

The atypical lipomatous tumor (ALT)/well-differentiated liposarcoma (WDLS) and the de-differentiated liposarcoma (DDLS) represent the most common category of liposarcomas. ALT/WDLSs and DDLSs are often difficult to distinguish from other tumors with similar morphological characteristics. In this study, we investigated whether the detection of amplified or overexpressed murine double-minute 2 (MDM2) can be a useful diagnostic ancillary aid. We used fluorescent in situ hybridization (FISH) and immunohistochemistry (IHC) to detect MDM2 amplification and protein overexpression, respectively, in 49 WDLSs, 5 DDLSs, 23 myxoid liposarcomas, 25 benign lipomatous tumors, and 75 spindle and pleomorphic sarcomas. MDM2 amplification was detected in 48 of 49 WDLSs, 5 of 5 DDLSs, 2 of 9 malignant peripheral nerve sheath tumors, and 2 of 10 myxofibrosarcomas. We did not detect MDM2 amplification in any of the benign lipomatous tumors. FISH-mediated detection of MDM2 amplification was the most valuable diagnostic aid for ALT/WDLS, as determined by using the Fisher exact test to compare two different diagnoses of 19 biopsies. On the contrary, unequivocal nuclear overexpression of MDM2 was found in only 10 of 50 ALT/WDLSs. The sensitivity and specificity of MDM2 amplification in distinguishing a DDLS from spindle and pleomorphic sarcomas were 100% and 95%, respectively, while those of MDM2 overexpression were 100% and 87%, respectively. In conclusion, our results indicate that FISH-mediated detection of MDM2 amplification is the most useful adjunct in the diagnosis of both ALT/WDLS and DDLS. However, IHC-mediated detection of MDM2 protein is useful only for the diagnosis of DDLS.     

The CDKN2A/CDKN2B/CDK4/CCND1 pathway is pivotal in well-differentiated and dedifferentiated liposarcoma oncogenesis: an analysis of 104 tumors

The MDM2 and CDK4 genes are the main targets of chromosome 12 amplification in well-differentiated and dedifferentiated liposarcomas. Nevertheless, around 10% of these tumors do not amplify CDK4. To find substitutive alterations of CDK4 amplification, we analyzed a large series of liposarcomas by array-CGH, real-time genomic PCR, gene expression array, and real-time RT-PCR. We demonstrate that an alteration in the CDKN2A/CDKN2B/CDK4/CCND1 pathway is present in almost all cases without CDK4 amplification, thereby confirming the pivotal role of this pathway in liposarcoma oncogenesis. Moreover, we show that cell cycle and differentiation are driven by a subtle and complex balance between members of this pathway. Finally, we demonstrate that in tumors without amplification/overexpression of CDK4, the chromosome 1q21-1q23 region is a preferential partner of chromosome 12 amplicon, suggesting that the mechanism of amplification is slightly different in this group of tumors.     

MDM2 gene amplification correlates with ring chromosomes in soft tissue tumors

The human homolog of the murine double minute type 2 gene (MDM2) has been cloned and mapped to 12q 13-14. The gene presumably functions as a cellular regulator and mediator of TP53 function. Amplification of the MDM2 gene has recently been observed in soft tissue sarcoma and in osteosarcoma. We studied MDM2 amplification in a series of 94 mesenchymal tumors and found 3-20-fold amplification in 20 tumors: in 10 of 49 malignant fibrous histiocytomas (MFH), in 1 of 2 pleomorphic liposarcomas, in 6 of 7 atypical lipomas, and in 3 of 12 typical lipomas. Normal hybridization patterns were detected in all 16 myxoid liposarcomas, in all 3 leiomyosarcomas, and in all 5 leiomyomas studied. The MDM2 amplification correlated with the presence of marker ring chromosomes; of the 10 MFH with MDM2 amplification, 5 had ring chromosomes, compared to 4 of 39 without MDM2 amplification, and all 9 lipomas with MDM2 amplification had ring chromosomes, in 5 of the tumors as the sole karyotypic anomaly. The correlation between ring chromosomes and MDM2 gene amplification indicates that the marker rings of MFH and of atypical lipoma often harbor genetic material derived from chromosome 12. Genes Chrom Cancer 9:26 1-265 (1994). © 1994 Wiley-Liss, Inc.     

Combined comparative genomic hybridization and genomic microarray for detection of gene amplifications in pulmonary artery intimal sarcomas and adrenocortical tumors

Identification of gene amplifications in human tumors is important for the understanding of tumorigenesis and may lead to discovery of diagnostic and prognostic markers. In this study, we used a microarray-based comparative genomic hybridization (CGH) technique, combined with conventional CGH, to identify gene amplifications in 43 tumors including eight pulmonary artery intimal sarcomas and 35 adrenocortical tumors. Conventional CGH revealed gains or amplifications of 12q13-q15 in six sarcomas and in two adrenocortical carcinomas. Using microarrays, we demonstrated that, among genes located on 12q13-q15, SAS/CDK4 were amplified in six sarcomas, and MDM2 and GLI in five and four sarcomas, respectively. The two adrenocortical tumors showed coamplifications of SAS/CDK4 and MDM2. Furthermore, PDGFRA (located on 4q12) amplification was identified in five sarcomas. Our data demonstrate: (1) amplifications of SAS/CDK4, MDM2, GLI, and PDGFRA are strongly associated with the tumorigenesis of pulmonary artery intimal sarcomas, whereas SAS/CDK4 and MDM2 coamplification may contribute to the progression of adrenocortical tumors; (2) microarray-based CGH is a useful tool for simultaneous detection of multiple gene amplifications, with a high sensitivity and resolution compared to that of conventional CGH.     

Molecular abnormalities in liposarcoma: role of MDM2 and CDK4-containing amplicons at 12q13–22

It has recently been shown that mdm2 overexpression with stabilization of p53 represents a characteristic of retroperitoneal well-differentiated-dedifferentiated, here renamed evolved (WD-E), liposarcomas at the immunocytochemical, molecular, and cytogenetic level. This make-up appears to be confined to half the cases in non-retroperitoneal well-differentiated liposarcomas. Since in different tumours MDM2 amplification involves amplicons encompassing flanking genes, such as CDK4, the possibility was investigated that in these tumours, CDK4 could act as an alternative or additional gene involved in the transformation mechanism. Forty-one retroperitoneal (R)/non-retroperitoneal (NR) well-differentiated-dedifferentiated (WD-DD) and 33 myxoid/round cell liposarcomas were reanalysed by immunocytochemical, molecular (nine cases) and fluorescence in situ hybridization (FISH) (one case) techniques. The results showed that all but one R WD-E cases carried the mdm2+, p53+, cdk4+ immunophenotype. In NR-WD liposarcomas, this immunophenotype was shared in five cases and the remainder showed mdm2+, p53−, cdk4+ in four and mdm2−, p53−, cdk4+ in one case, showing ring chromosomes by FISH analysis. TP53 mutations are confirmed to be closely correlated with NR-DD liposarcomas and no CDK4 involvement was found in the myxoid/round cell liposarcoma group. As well as confirming the synergistic effect of MDM2 and CDK4, these results are consistent with the concept that amplicon(s) excluding MDM2 may contribute to transformation and support a role of CDK4 in opposing p53 function, particularly in NR WD liposarcoma. © 1998 John Wiley & Sons, Ltd.     

Dedifferentiated liposarcoma with rhabdomyoblastic differentiation

Dedifferentiated areas of dedifferentiated liposarcoma (DDL) usually show malignant fibrous histiocytoma (MFH)- or fibrosarcoma-like features and lack any histologic signs of specific differentiation. However, some reports have demonstrated specific differentiation in these areas, with histologic features resembling those of rhabdomyosarcoma, leiomyosarcoma, and osteosarcoma. We report here a pathologic and genetic analysis of three cases of DDLs with rhabdomyosarcomatous areas. MFH- or fibrosarcoma-like areas of one primary DDL and two recurrent DDLs contained various amounts of rhabdomyoblasts, which were immunoreactive for desmin, myoglobin, muscle actin (HHF-35), and myogenin. An ultrastructural examination demonstrated rhabdomyoblasts with abundant cytoplasm containing thin and thick filaments and Z-bands. By real-time PCR, amplification of mdm2 and cdk4 was confirmed in both well-differentiated and dedifferentiated areas with rhabdomyoblasts of all cases. To our knowledge, only seven cases of DDLs with rhabdomyosarcomatous components have been reported, and furthermore, the genetic profiles of the rhabdomyosarcomatous components in DDLs have not been investigated. This study demonstrates that DDLs with rhabdomyosarcomatous areas have genetic alterations that are common to well-differentiated/dedifferentiated liposarcomas.     

Significance of loss of heterozygosity of the RB1 gene during tumour progression in well-differentiated liposarcomas

Tumour progression can be investigated in liposarcomas showing a transition from a low-grade well-differentiated (WD) to a high-grade dedifferentiated (DD) variant. As RB1 gene alterations are common defects in sarcomas, this study examined the frequency of RB1 loss of heterozygosity (LOH) in a group of 14 well-differentiated liposarcomas (WDLs) and 17 well-differentiated/dedifferentiated liposarcomas (WD/DDLs), using a microdissection approach (PALM laser pressure catapulting) that allows the two histological components to be separated for polymerase chain reaction (PCR) analysis. In addition, RB1 protein expression and the Mib1 proliferation index were determined by immunohistochemistry and interphase FISH was performed with an RB1 probe at 13q14. By the use of four intragenic polymorphic RB1 markers (introns 1, 17, 20, and 25) for PCR, allelic losses were found only in the DD parts, but never in the pure WDLs or in the WD components of the WD/DDLs investigated. Furthermore, DD areas characterized by a heterogeneous RB1 protein expression pattern (35-65% immunopositivity), as compared with 90-100% RB1 positivity in WD areas, showed a marked increase in Mib1 proliferation index (19.6% versus 1.8% in WD areas; p<0.001). Interphase fluorescence in situ hybridization (FISH) detected a higher RB1-LOH rate in the DD components of WD/DDLs. Considering the different detection sensitivities of the three methodologies, it is concluded that loss of RB1 function already begins in the WDL, and that the tumour cell population with RB1-LOH starts prevailing in the tumour mass during progression of a WDL.     

Genomic alterations in sarcomas: a histologic correlative study with use of oncogene panels.

Amplification and rearrangement of cellular proto-oncogenes are two of the several possible genetic alterations implicated in carcinogenesis and tumor progression. Although morphologically similar tumors may be heterogeneous at the level of the genome, some tumor types have shown relatively frequent and consistent abnormalities of specific oncogenes. In order to determine the frequency of oncogene amplification and rearrangement in several types of human sarcomas and to determine if histologically similar tumors have common genetic alterations, we analyzed 26 primary sarcomas by Southern hybridization. The oncogene probes utilized were N- and H-ras, sis, EGF-R (erb-B-1), neu (erb-B-2), fos, N- and c-myc, mos, and yes. The tumors studied included: five rhabdomyosarcomas (one alveolar, four embryonal), six malignant fibrous histiocytomas, six leiomyosarcomas, four liposarcomas, two Ewing's sarcomas, one osteosarcoma, and two fibrosarcomas. Oncogene abnormalities were identified in three tumors. One rhabdomyosarcoma showed 12-fold amplification and concurrent rearrangement of sis. This particular tumor also revealed rearrangement of H-ras and 15-fold amplification of c-myc. A second rhabdomyosarcoma revealed rearrangement of neu. A liposarcoma had a sis rearrangement. These findings suggest that many sarcomas show no common structural oncogene abnormalities. The presence of differing oncogene alterations within the rhabdomyosarcoma group indicates genetic heterogeneity among histologically similar sarcomas. The finding of a sis rearrangement in both a liposarcoma and a rhabdomyosarcoma, however, may suggest common oncogenesis among different tumor types.     

DISTINCT mdm2/p53 EXPRESSION PATTERNS IN LIPOSARCOMA SUBGROUPS: IMPLICATIONS FOR DIFFERENT PATHOGENETIC MECHANISMS

Recent findings have indicated that TP53 inactivation in sarcomas may result from mutation and/or deletion of the TP53 gene or, alternatively, from binding to the MDM2 gene products. To investigate further a possible role of the two genes in sarcomas, 24 large and deep-seated lipomas and 74 liposarcomas of various subtypes were analysed for mdm2 and p53 overexpression by immunocytochemistry. Nineteen cases of the same series were also molecularly analysed for both MDM2 gene amplification and TP53 mutations, and a further ten cases for non-random chromosomal abnormalities. In the retroperitoneal well-differentiated–dedifferentiated (WD–DD) group, 15/16 WD and 8/8 DD liposarcomas displayed the mdm2+/p53+ phenotype, consistent with MDM2 gene amplification in the absence of TP53 mutations. In the non-retroperitoneal WD–DD group, 5/11 WD liposarcomas also retained the mdm2+/p53+ phenotype whereas all DD liposarcomas showed an immunophenotype and, when assessed, a genotype consistent with mutant TP53. Null mdm2 immunophenotype, coupled with evidence of a specific chromosome translocation t(12;16), was constantly observed in both the usual and the cellular subtypes of myxoid liposarcoma, three cases of which also showed TP53 alterations at the genetic or protein level. Neither mdm2 nor p53 overexpression was observed in the lipomas. The results show the existence of three main pathogenetically distinct groups of liposarcoma. The first retroperitoneal WD–DD group, which represents a novel class of tumours within a single histological category of sarcoma, where MDM2-mediated inactivation of p53 could be related to the pathogenetic mechanism. The second is the non-retroperitoneal WD–DD group, where the TP53 mutations appear to correlate with the dedifferentiation process. The third is the myxoid group, which is characterized by its own unique cytogenetic profile and never shows any involvement of TP53 or MDM2 genes. As for diagnostic significance, the absence of mdm2 and p53 reactivity in lipomas seems to represent a useful marker for differential diagnosis from lipoma-like WD liposarcomas. © 1997 by John Wiley & Sons, Ltd.     

伴有脑膜上皮细胞样旋涡状特征的去分化脂肪肉瘤六例临床病理学观察

目的探讨伴有脑膜上皮细胞样旋涡特征的去分化脂肪肉瘤(dedifferentiated liposarcomas with meningothelial-like whorls,DDLMW)的组织形态学、免疫组织化学及分子遗传学特征。方法收集江苏省人民医院(南京医科大学第一附属医院)2012年3月至2018年8月诊断为DDLMW的患者6例病历资料及存档切片,采用免疫组织化学染色检测MDM2、CDK4、p16等,应用荧光原位杂交(FISH)法检测MDM2基因扩增情况,并复习相关文献。结果患者男性3例,女性3例;4例发生于后腹膜,2例发生于纵隔,发病年龄范围40~77岁(中位年龄58岁)。大体表现为巨大单发或多发结节状肿块,镜下除了可见高分化脂肪肉瘤成分之外,均可见具有特征性的旋涡样结构,形态类似脑膜瘤;旋涡小体肿瘤细胞梭形或卵圆形,同心圆状致密排列,轻-中度异型性;此外,4例在旋涡小体的周围或中间可见化生性骨组织。免疫表型:肿瘤组织表达MDM2、CDK4、p16,不表达S-100蛋白、平滑肌肌动蛋白、SOX10、上皮细胞膜抗原、CD21、CD23、CD35;肿瘤细胞Ki-67阳性指数低。6例经FISH检测均显示肿瘤细胞伴有MDM2基因的扩增。结论DDLMW是一种罕见的去分化脂肪肉瘤的组织学亚型,特征性的旋涡状结构并不预示其有神经束膜或滤泡树突细胞的分化,认识并熟悉其存在结合免疫组织化学及MDM2基因FISH检测有助于其诊断与鉴别诊断。     

Primary retroperitoneal myxoid/round cell liposarcoma is a nonexisting disease: an immunohistochemical and molecular biological analysis

Almost all primary retroperitoneal liposarcomas can be classified as well-/dedifferentiated liposarcoma. Rarely, however, primary retroperitoneal liposarcoma is classified as myxoid/round cell liposarcoma, based on the presence of myxoid areas and vascular crow's feet pattern, which has resulted in a debate on the classification of liposarcoma in the retroperitoneum. Genetically, myxoid/round cell liposarcoma and well-/dedifferentiated liposarcoma are different diseases. Myxoid/round cell liposarcoma is characterized by a translocation causing FUS-CHOP or EWSR1-CHOP fusion, whereas well-/dedifferentiated liposarcoma is characterized by an amplification of the 12q13-15 region, including MDM2 and CDK4 genes. As myxoid/round cell liposarcoma is highly radio- and chemosensitive, differentiation between subtypes is important to optimize treatment. We studied whether primary retroperitoneal liposarcomas diagnosed as myxoid/round cell liposarcoma represent molecularly true myxoid/round cell liposarcoma or are histopathological mimics and represent well-/dedifferentiated liposarcoma. Primary retroperitoneal myxoid/round cell liposarcoma (n=16) were compared to primary extremity myxoid/round cell liposarcoma (n=20). Histopathological and immunohistochemical features were studied. Amplification status of the 12q13-15 region was studied using a multiplex ligation-dependent probe amplification analysis, and FUS-CHOP or EWS-CHOP translocations were studied using RT-PCR. In primary retroperitoneal myxoid/round cell liposarcoma, MDM2 and CDK4 staining was both positive in 12 of 15 cases. In primary extremity myxoid/round cell liposarcoma, MDM2 was negative in 18/20 and CDK4 was negative in all cases. Multiplex ligation-dependent probe amplification showed the amplification of 12q13-15 region in 16/16 primary retroperitoneal myxoid/round cell liposarcomas and in 1/20 primary extremity myxoid/round cell liposarcomas. Translocation was present in all (18/18) primary extremity myxoid/round cell liposarcomas, but absent in all primary retroperitoneal myxoid/round cell liposarcomas. On the basis of immunohistochemical and molecular characteristics, apparent primary retroperitoneal myxoid/round cell liposarcoma can be recognized as well-/dedifferentiated liposarcoma with morphological features mimicking myxoid/round cell liposarcoma. In these cases, treatment should probably be specifically designed as for well-/dedifferentiated liposarcoma. Moreover, finding of myxoid/round cell liposarcoma translocations in a retroperitoneal localization is highly suggestive of metastasis and should prompt search for a primary localization outside the retroperitoneum.     

Atypical spindle cell lipoma: a clinicopathologic,immunohistochemical, and molecular study emphasizing its relationship to classical spindle cell lipoma

We studied a series of spindle cell lipomas arising in atypical sites and showing unusual morphologic features (which we called atypical spindle cell lipoma) to assess if these lesions have the same chromosomal alterations as classical spindle cell lipoma but different from those found in atypical lipomatous tumor/well-differentiated liposarcoma. We investigated alterations of different genes in the 13q14 region and the amplification status of the MDM2 and CDK4 genes at 12q14-15 by multiplex ligation-dependent probe amplification (MLPA) and fluorescence in situ hybridization (FISH) analysis. In the atypical spindle cell lipomas, MLPA revealed deletions in the two nearest flanking genes of RB1 (ITM2B and RCBTB2) and in multiple important exons of RB1. In contrast, in classical spindle cell lipomas, a less complex loss of RB1 exons was found but no deletion of ITM2B and RCBTB2. Moreover, MLPA identified a deletion of the DLEU1 gene, a finding which has not been reported earlier. We propose an immunohistochemical panel for lipomatous tumors which comprises of MDM2, CDK4, p16, Rb, which we have found useful in discriminating between atypical or classical spindle cell lipomas and other adipocytic neoplasms, especially atypical lipomatous tumor/well-differentiated liposarcoma. Our findings strengthen the link between atypical spindle cell lipoma and classical spindle cell lipoma, and differentiate them from atypical lipomatous tumor/well-differentiated liposarcoma.     

Aspiration cytology of lipomatous tumors: A 10-year experience at an orthopedic oncology center

The cytodiagnoses of preoperative fine-needle aspirate smears from 72 histologically proven lipomatous tumors (52 lipomas and 20 liposarcomas of varying type) collected during the 10-yr period 1972–1981 were correlated to the corresponding histopathologic diagnoses. Three out of 52 lipomas were erroneously diagnosed as low-grade malignant liposarcomas, and one out of 20 liposarcomas was falsely diagnosed as a benign soft-tissue tumor. Of the 20 liposarcomas, 15 were cytologically diagnosed as such, and the majority of the myxoid and the pleomorphic liposarcomas were correctly diagnosed as to type. Important differential diagnostic problems were, on one hand, the separation of lipoma with regressive changes and histiocytic reaction and lipoma with chondroid metaplasia from low-grade malignant liposarcoma and, on the other hand, liposarcoma from intramuscular myxoma, myxofibrosarcoma, and malignant fibrous histiocytoma. The differential diagnosis of liposarcoma as opposed to other soft-tissue sarcomas is discussed, and it is concluded that preoperative fine-needle aspiration of lipomatous tumors is of value in the management of these tumors. Diagn Cytopathol 1987;3:295–302.     

Molecular cytogenetic analysis of complex karyotypes with derivative chromosome der(1)t(1;5) found in two patients with myeloid leukemia

Dedifferentiated liposarcoma of the pleura is an extremely rare malignancy mimicking a variety of tumors, such as other sarcomas, mesothelioma, and malignant solitary fibrous tumor of the pleura. Liposarcoma of the pleura can be combined with mediastinal involvement, and in most cases it may be impossible to be certain where the primary tumor originated. In this report, we describe a very rare occurence of a dedifferentiated liposarcoma of the pleura in a 76-year-old woman associated with a distinct second dedifferentiated liposarcoma of the mediastinum. Histologically, the pleural tumor demonstrated spindle cells arranged in a fascicular pattern, whereas the mediastinal tumor was mostly adipocytic with small areas of spindle cells. Vimentin and protein S100 were focally expressed by the tumor cells. The differential diagnosis of the pleural mass included malignant solitary fibrous tumor. Cytogenetic analysis showed supernumerary ring chromosomes in the pleural tumor, as well as strong amplification of MDM2 and CDK4 genes in both tumors. Array comparative genomic hybridization showed amplifications of chromosome arms 6q, 12q, and 15q, shared by both tumors and strongly pointing to a common origin.     

Amplification of CDK4 and MDM2 in malignant melanoma

Amplification of the 12q13-15 region is a common event in several human tumors including liposarcomas, gliomas, and osteosarcomas. We have demonstrated high-level amplification of 12q14 in a subset of uncultured malignant melanomas (3 of 53). High-resolution mapping of the amplicon using quantitative PCR revealed a bipartite amplicon consisting of a primary 50-kb amplicon centered on CDK4 and a secondary amplicon centered on MDM2, without amplification of the intervening 11 Mb of genomic DNA. Analysis of mRNA and protein levels in melanomas with 12q14 amplification demonstrated overexpression of target genes CDK4 and MDM2 without loss of CDKN2A-P16 (P16INK4A) or CDKN2A-P14ARF (P14ARF) expression, important regulators of the RB1 and TP53 pathways, which are commonly lost or mutated in melanoma. These results suggest that coamplification of CDK4 and MDM2 may substitute for loss of P16INK4A and P14ARF function in a subset of melanomas.     

Immunostaining for peroxisome proliferator gamma distinguishes dedifferentiated liposarcoma from other retroperitoneal sarcomas.

Dedifferentiated liposarcoma can be readily diagnosed by the juxtaposition of a well-differentiated liposarcoma to a nonlipogenic sarcoma. However, if the lipogenic component is not abundant due to surgical sampling or small biopsy, dedifferentiated liposarcoma can be difficult to distinguish from other poorly different sarcomas. Peroxisome proliferator-activated receptor gamma (PPAR-gamma) is a nuclear hormone receptor that plays a critical role in adipocyte differentiation. Prior studies have not only demonstrated PPAR-gamma mRNA in various subtypes of liposarcoma but have also shown that adipocyte differentiation can be induced in some liposarcomas by a PPAR-gamma agonist. In the present study, we investigated whether immunostaining for PPAR-gamma can be used to distinguish dedifferentiated liposarcoma from other retroperitoneal sarcomas. We examined a series of 40 dedifferentiated liposarcoma and compared the staining for PPAR-gamma to a series of 24 retroperitoneal sarcomas that lacked lipogenic differentiation. A monoclonal antibody against PPAR-gamma was used to stain formalin-fixed paraffin-embedded tissue. Specific nuclear immunostaining was present in 37/40 (93%) of the dedifferentiated liposarcoma and 6/24 (25%) of the other sarcomas (two leiomyosarcomas and four undifferentiated sarcomas). Interestingly, immunostaining for CDK4 and/or MDM2 was identified in three of the four PPAR-gamma-positive undifferentiated sarcomas, raising the possibility that these may represent dedifferentiated liposarcoma. This is the first study demonstrating the utility of PPAR-gamma immunohistochemistry in the diagnosis of dedifferentiated liposarcoma in tissue sections. Although not completely specific, the presence of PPAR-gamma staining, in combination with histologic findings and other markers, can aid in the diagnosis of dedifferentiated liposarcoma, particularly on small biopsies that may not sample the well-differentiated component.     

Telomere lengths of translocation-associated and nontranslocation-associated sarcomas differ dramatically

Sarcomas can be divided into those with specific translocations displaying monotonous cytomorphology, and those with complex karyotypes and marked cellular pleomorphism. Telomeres contain terminal DNA sequence repeats that maintain chromosomal stability. Telomeres shorten with cell division and may become dysfunctional leading to chromosomal instability. Using a fluorescence in situ hybridization/immunofluorescence method to assess telomere lengths in archival tissues we analyzed these two types of sarcomas using paraffin-embedded primary tumor specimens. Tissues from nine sarcomas with characteristic translocations (two synovial sarcomas, two alveolar rhabdomyosarcomas, two desmoplastic round cell tumors, and one each of infantile fibrosarcoma, myxoid liposarcoma, cellular congenital mesoblastic nephroma) and nine without (four malignant fibrous histiocytomas, two leiomyosarcomas, one pleomorphic rhabdomyosarcoma, one dedifferentiated chondrosarcoma, and one malignant peripheral nerve sheath tumor) were analyzed. In all (nine of nine) cases with specific translocations, which generally have few karyotypic abnormalities, telomere lengths were similar to or reduced compared to surrounding nonneoplastic tissues. In contrast, telomeres in cases lacking specific translocations, which generally contain complex karyotypes, were often found to be dramatically lengthened and heterogeneous. In addition to markedly elongated telomeres, seven of nine (78%) complex cases exhibited large brightly stained regions corresponding to a specific type of promyelocytic leukemia nuclear body found in immortalized cells that maintain telomeres in a telomerase-independent manner [alternative lengthening of telomeres (ALT) pathway]. This phenotype is unlike that of epithelial neoplasms that typically display complex karyotypes with abnormally short telomeres maintained by the enzyme telomerase. The discovery of heterogeneous telomere lengths and evidence of the ALT pathway in the majority of sarcomas with complex karyotypes supports the existence of a telomere maintenance pathway incapable of full karyotypic stabilization in pleomorphic sarcomas. These findings provide additional molecular-genetic evidence supporting the dichotomous grouping of sarcomas into those with characteristic signature translocations without extensive additional karyotypic abnormalities, and those without such signature translocations that typically display very complex karyotypes, and point to telomere dysfunction as a plausible contributor to the chromosomal aberrations found in complex sarcomas.